To cut or drill a brittle work piece such as stone, bricks, concrete and asphalt requires abrasive particles having higher hardness than a work piece.
The abrasive particles are exemplified by artificial diamond particles, natural diamond particles, nitrogen boride and super-hardness particles, of which artificial diamond particles are most widely used.
An artificial diamond (hereinafter referred to as “diamond” was invented in the 1950s. The diamond, which is known to have the highest hardness out of materials in the earth, has been accordingly used for cutting and grinding tools due to such properties.
Especially, the diamond has been broadly used in a stone processing field where stone such as granite and marble is cut and ground, and in a construction field where a concrete structure is cut and ground.
A cutting segment and a cutting tool, which will be explained hereunder, employ diamond particles as abrasive particles.
Typically, a diamond tool comprises segments having diamond particles dispersed therein and a metal core having the segments fixed thereto.
FIG. 1 illustrates an example of a segment type diamond tool.
As shown in FIG. 1, the segment type diamond tool 1 includes a plurality of segments 11 and 12 fixed to a disk-shaped metal core 2, in which each of the segments 11 and 12 has diamond particles 5 randomly dispersed therein.
The segments are fabricated via powder metallurgy in which the segments are mixed with metal powder, molded and then sintered.
In case of mixing the diamond particles with the metal powder as just described, the diamond particles are not evenly dispersed among the metal powder but randomly dispersed inside the cutting segment.
In the cutting tool having the cutting segment, its cutting rate is contradictory to its useful life.
For example, in case of using the metal powder with low abrasion resistance to enhance cutting rate, useful life of the cutting segment is shortened. In contrast, in case of using the metal powder with high abrasion resistance to extend useful life, the diamond particles blunted during cutting do not easily fall off, thus lowering cutting rate.
In addition, in case of mixing the diamond particles with the metal powder serving as a bond as just described, the diamond particles are not uniformly dispersed owing to differences between metal powders and diamond particles in terms of particle size and specific gravities. Therefore, as shown in FIG. 1, this disadvantageously leads to a cutting surface 3 having too many diamond particles or a cutting surface 4 having too few diamond particles, causing the diamond particles to segregate.
To overcome such problems, a cutting segment having diamond particles uniformly arranged has been suggested as shown in FIG. 2.
FIG. 2 (b) is a cross-sectional view of a cutting segment taken along the line A-A in FIG. 2(a), when used during a cutting process.
As shown in FIG. 2 (a), the cutting segment 20 has diamond particles 25 arranged in rows 21 in a cutting direction (in a length direction of the cutting segment). The diamond rows 21 are disposed in a width direction of the cutting segment to form a plurality of diamond particle layers 31 as shown in FIG. 2(b). The diamond layers are stacked in a thickness direction of the cutting segment.
As shown in FIG. 2 (b), the diamond particle layers 31 of the diamond particle rows 21 having the diamond particles 25 arranged are uniformly spaced apart from each other. In case of using the diamond particles smaller than a gap D between the diamond particle layers, the diamond layers 31 have an area without the diamond particles 41 therebetween.
In cutting a work piece via the cutting segment 20, blank sections are worn away first, thus generating grooves. The depth h of the grooves increases in proportion to the gap D between the diamond particle rows. If the depth h of the grooves of the blank sections is ⅔ of the average diameter of the abrasive particles, the diamond particles 25 easily fall off due to decline in retention by the metal powder.
Meanwhile, a small depth of the grooves improves useful life of the cutting segment but diminishes cutting rate owing to low protrusion of the abrasive particles.
In this fashion, the cutting segment 20 prevents the diamond particles 25 from segregating, thereby maximizing work efficiency for the diamond particles 25. Also, cutting rate can be boosted through a special concept of a “shoveling effect.” However, due to the diamond particle rows equally spaced apart from each other, with increase in the depth h of the groove, the metal powder cannot sufficiently retain the diamond particles 25 so that the diamond particles are easily discharged during cutting.
In the end, the diamond particles 25 fall off not by abrasion but by a lacking retention power despite their cutting capability. This disadvantageously reduces useful life, especially for a work piece cut into large debris.